1. Field of the Invention
The present invention relates to a passenger seat device that includes a detector for detecting whether a seat is occupied and a seat heater covered with a waterproof sheet, and to a method of manufacturing the same.
2. Description of Related Art
JP-A-2003-80989 proposes a device for detecting whether a passenger seat of an automotive vehicle is occupied or not. In this device, a passenger on the seat is detected based on changes in an alternating current electromagnetic field in the vicinity of the seat, particularly at a portion above the seat. This type of the detector is referred to as a capacitance-type detector. The detector includes a transmitting electrode embedded in the seat for forming the electromagnetic field and a receiving electrode embedded in a seat-back. A capacitive impedance between the transmitting electrode and receiving electrode decreases when a passenger occupies the seat. Thus, whether the seat is occupied or not is detected.
The capacitance-type detector described in JP-A-2003-80989 also includes a seat heater embedded in the seat at a position under the transmitting electrode (also referred to as a detector electrode). When both of the seat heater and the detector electrode are embedded in a seat as in this example, the seat heater having a substantially constant potential under alternating current is positioned in the vicinity and under the detecting electrode.
In this detector, there is a problem that an impedance between the detector electrode and the seat heater varies if water permeates into the seat and reaches the seat heater. The permeation of water may be caused by rain entering into a passenger compartment or water spilled on a seat surface. Whether the seat is occupied or not may not be accurately detected if water reaches the seat heater located underneath the detector electrode. The impedance between the detector electrode and the seat heater is considerably lowered by the permeated water because water has a high relative dielectric constant.